1. Introduction 2 Division of buildings in compartments Three
types of criteria should be fulfilled : insulation, integrity and
resistance. Fire in a building cause deaths and destruction of
goods (Department Store Innovation , 1967).
Slide 3
1. Introduction 3 Then, global behaviour of steel structures
without focusing on the behaviour of connections because : a)
Exposure of joints to fire is lower than for beams and columns. 90s
: fire research focused on the single elements. b) More material is
concentrated in the joint zone Conclusion : A same level of fire
protection for joints and structural elements was considered as
sufficient
Slide 4
1. Introduction Cooling phase : key issue for the fire
resistance of steel structures (WTC, Cardington, Coimbra tests,)
4
Slide 5
1. Introduction Development of tensile forces due to axial
restraints and plastic deformations Limited ductility of bolts and
welds components when joint resistance is not sufficient Bolts and
welds strengths under fire decreases faster than the carbon steel
strength 5
Slide 6
1. Introduction 6 Behaviour of bolts and welds at elevated
temperatures (Riaux, Kirby, Latham) Behaviour of bolted joints
(Wainman, Universities of Manchester and Sheffield) Investigations
about the influence of connections behaviour on the performance of
beams under fire (University of Manchester)
Slide 7
1. Introduction 7 7th Cardington test Investigations on rigid
and semi-rigid connections under natural fire (University of
Coimbra) The objective of the present work is to focus on the
behaviour of simple steel connections (and of connected beams)
under natural fire.
Slide 8
Overview of the thesis 8 1. Introduction 2. Distribution of
temperature in joints 3. Prediction of internal forces in steel
joints under natural fire 4. Experimental tests and models for the
behaviour of connection components under heating/cooling 5.
Experimental tests and numerical investigations for the mechanical
behaviour of steel connections under natural fire 6. General
conclusions and perspectives
Slide 9
Academic year 2009-2010 9
Slide 10
2. Distribution of temperature 10 Time-temperature curve
divided in four stages Analytical models, Zone models and Field
models to predict the distribution of temperature of the
compartment
Slide 11
2. Distribution of temperature 11 Lumped Capacitance Method for
steel members (EN 1993-1-2 and EN 1994-1-2) + joints (Annex D of EN
1993-1-2) Temperature profile of joints covered by a concrete slab
(EN 1993-1-2)
Slide 12
2. Distribution of temperature 12 Uniform temperature in the
zone considered Heat exchanges between the steel section and the
concrete slab are not taken into account (adiabatic) Zone
considered for joints not defined accurately
Slide 13
2. Distribution of temperature 13
Slide 14
2. Distribution of temperature 14
Slide 15
2. Distribution of temperature 15 Adapted to ISO curve Ratios
independent of time Geometry of the joint not considered in
detail
Slide 16
2. Distribution of temperature 16 Predict temperature at
flanges levels accounting for the presence of the concrete slab
Profile of interpolation for temperature between flanges
Adaptations to existing methods or new methods Validations against
numerical simulations under heating and cooling phases
Slide 17
2. Distribution of temperature 17 Case nBeamColumnPlate 1IPE
300HEA 300200*380*10 2IPE 550HEM 300410*625*25 ISO and parametric
fires IPE 180 to IPE 550 sections
Slide 18
2. Distribution of temperature 18 Lumped capacitance Method :
(A m /V) of the flange Point of reference
Slide 19
2. Distribution of temperature 19 Point of reference Lumped
Capacitance Method : (A m /V) joint = (A m /V) beam /2 IPE 300
configuration
Slide 20
2. Distribution of temperature 20 Lumped Capacitance Method :
(A m /V) of the flange (3 sides heated) Point of reference IPE 300
beam
Slide 21
2. Distribution of temperature 21 Composite Section Method
Slide 22
2. Distribution of temperature 22 Composite Section Method
HeatingHeating + Cooling
Slide 23
2. Distribution of temperature 23 Heat Exchange Method Lumped
Capacitance Method T 1, T 2 : Temperatures of the top and bottom
flanges x : Length of heat transfer (chosen equal to the root
fillet)
Slide 24
2. Distribution of temperature 24 Heat Exchange Method Graph n1
: IPE 300 beam = 1 t heating = 30 min Graph n2 : IPE 550 beam = 1 t
heating = 30 min Graph n3 : IPE 550 beam = 1 t heating = 60
min
Slide 25
2. Distribution of temperature 25 Lumped Capacitance Method :
(A m /V) joint = (A m /V) beam /2 Composite Section Method
Slide 26
2. Distribution of temperature 26 Heat Exchange Method Lumped
Capacitance Method T 1, T 2 : Temperatures of the top and bottom
flanges
Slide 27
2. Distribution of temperature 27 Heat Exchange Method Graph n1
: Heating Beam section : IPE 300 Graph n2 : Heating + Cooling Beam
section : IPE 300
Slide 28
2. Distribution of temperature 28 Reference Lines 2-D3-D
Temperature profile suggested (beam + joint) Graph n1 : ISO
(Heating) Graph n2 : Param (Cooling) A. Beam IPE 300 B. Joint IPE
300
Slide 29
2. Distribution of temperature 29 Lumped Capacitance Method
Composite Section Method Heat Exchange Method
Slide 30
Academic year 2009-2010 30 N M V
Slide 31
3. Prediction of internal forces 31 In real cases :
superposition of axial forces and bending moments due to
non-uniform elevation of temperature. A
Slide 32
3. Prediction of internal forces 32 Vertical deflections induce
beam shortening or axial forces The combination of axial forces and
vertical deflections influences the distribution of bending moments
Equilibrium must be stated in the deformed configuration Yin
(2005)
Slide 33
3. Prediction of internal forces 33 All terms are function of
the mid-span deflection m,max Pinned : Rigid : Semi-rigid :
Deflection profile : Axial force : where :
Slide 34
3. Prediction of internal forces 34 All terms are function of
the mid-span deflection m,max Mid-span bending moment : Support
bending moment : Inelastic interaction :
Slide 35
3. Prediction of internal forces 35 All terms are function of
the mid-span deflection m,max Adaptations for non-uniform profiles
of temperature : Pinned : Rigid : Semi-rigid : where :
Slide 36
3. Prediction of internal forces 36 Consideration of the
elliptic branch for evaluation of F T (f p, f y, E)(F propor, F pl,
K A ) LmLm F L m,propor L m,pl F pl F propor
Slide 37
3. Prediction of internal forces 37 Consideration of the
elliptic branch for evaluation of M T and M R based on the
development of a method to predict the (M diagram of a beam section
under axial force and a non-uniform distribution of
temperature.
Slide 38
3. Prediction of internal forces 38 Comparison with FE model
(SAFIR) with fibre elements
Slide 39
3. Prediction of internal forces 39 Expression of the
thermally-induced bending moment M t Equation of compatibility : +
Limitation of the bending moment to M pl,beam and M pl,joint
Slide 40
3. Prediction of internal forces 40 Extensional stiffness of
the beam (2 nd order effects) F T,1 = 1 L Pinned connections Rigid
connections
Slide 41
3. Prediction of internal forces 41 Coefficient of
interpolation between deflection profiles with pinned and rigid
connections evaluated by stating the equilibrium between the
bending moments at the beam extremity and the joint. Equilibrium L
= 5m IPE 300 beam w = 10 kN/m K R = 10.000 kN.m/rad
Slide 42
3. Prediction of internal forces 42 Rugby goal post
sub-structure 2 tests on simply-supported beams 3 tests on
sub-structures with web-cleats connections 10 tests on
sub-structures with flush end-plate connections Flush End-plate Web
Cleats
Slide 43
3. Prediction of internal forces 43 Mechanical Analysis :
Simply-supported beams T critical if T is uniform
3. Prediction of internal forces 45 Mechanical Analysis :
Sub-structures with flush end-plate connections K A = 8 kN/mm
Mid-span deflections : Axial Force : Hogging Bending Moment :
Slide 46
3. Prediction of internal forces 46 1. Simply-supported beam -
Non-uniform distribution of T DeflectionsAxial ForceBending
Moments
Slide 47
3. Prediction of internal forces 47 2. Bilinear rotational
restraints - Non-uniform distribution of T DeflectionsAxial Force
Bending Moments Mid-span Support
Slide 48
3. Prediction of internal forces 48 Modifications n1 & 2 :
Elliptic branch of the stress-strain diagram of carbon steel for
(F, L m ) and (M, m ) diagrams 6 meter-long IPE 300 beam (S275)
Distribution of T : Ratios 0.8 1 1.2 K R = 3000 kN.m/rad (elastic)
w = 0.5 K = 3% Degree of accuracy enhanced Better convergence at
the transition bending - catenary
Slide 49
3. Prediction of internal forces 49 Analysis of the influence
of the proposed modifications Modification n3 : Expression of the
thermally-induced bending moment M t Aimed at extending the field
of application of the Modified Method !
Slide 50
3. Prediction of internal forces 50 Analysis of the influence
of the proposed modifications Modification n4 : Extensional
stiffness K A of the beam accounting for 2 nd order effects
Deformability of the beam
5. Tests and models of connections 77 10mm-thick plate IPE 300
beam Heated gradually until failure Flush end-plate connections 5.5
meter-long IPE 300 beam Thermally-protected HEA 220 column K = 1%
L.R. = 0.3 (theoretically) Test n1 (Metz) Test stopped at T furnace
= 840C (T bottom flange = 800C) Beam deflection > 220 mm No
failure of bolts
Slide 78
5. Tests and models of connections 78 10mm-thick plate IPE 300
beam Heated gradually until 700C before natural cooling Flush
end-plate connections 5.5 meter-long IPE 300 beam
Thermally-protected HEA 220 column K = 1% L.R. = 0.3
(theoretically) Test n2 (Metz) Beam deflection = 58 mm (constant
during cooling) No failure of bolts
Slide 79
5. Tests and models of connections 79 Heated gradually until d
= 200 mm before natural cooling Fin plate connections 4.4
meter-long IPE 300 beam Thermally-protected HEB 300 column K = 6.6%
L.R. = 0.3 (f y = 345 MPa) Test n3 (Delft) Temperature reached 650C
in the beam and 600C near the joint Failure of bolts after 127
minutes
Slide 80
5. Tests and models of connections 80 Heated gradually until d
= 200 mm before natural cooling Web cleats connections 4.4
meter-long IPE 300 beam Thermally-protected HEB 300 column K = 6.6%
L.R. = 0.3 (f y = 345 MPa) Test n4 (Delft) Temperature reached 670C
in the beam and 600C near the joint No failure of bolts
Slide 81
5. Tests and models of connections 81 The action of joints is
represented by beam elements including one fibre per bolt or
compressive row Cross-section of the beam element
Slide 82
5. Tests and models of connections 82 Fin plateWeb cleatsHeader
PlateFlush end-plate
Slide 83
5. Tests and models of connections 83 BILIN BILIN_COMP
Translated BILIN_COMP BILIN_BOLTSBILIN_ASYMBILIN_TENS Symmetric to
BILIN_COMP !
Slide 84
5. Tests and models of connections 84 Failure criteria 1.
Classes of ductility Plastic resistance of weakest ductile
component Ultimate resistance of weakest ductile component
Resistance of weakest brittle component Class A Class B Class C
Resistance Temperature
Slide 85
5. Tests and models of connections 85 Failure criteria
Criterion n1 : One fibre representing the action of a class C bolt
row is yielded or Criterion n2 : All the fibres representing the
action of bolt rows are yielded and at least one bolt row is class
B 2. Criteria Plastic resistance of weakest ductile component
Ultimate resistance of weakest ductile component Resistance of
weakest brittle component Class A Class B Class C Resistance
Temperature
Slide 86
5. Tests and models of connections 86 Test n1 (Metz)
Restraining system modelled by one element (elastic spring) f y =
355 MPa. f ub : 956 Mpa (tests at room T) - Experimentally, failure
after 70 min (T furnace = 797C) - Good correlation
Slide 87
5. Tests and models of connections 87 Test n2 (Metz) No
failure
Slide 88
5. Tests and models of connections 88 Test n3 (Delft) : Fin
plate connections Criterion n2 reached after 119 min.
Experimentally : failure after 127 min.
Slide 89
5. Tests and models of connections 89 Test n4 (Delft) : Web
cleats connections The weakest components are ductile No
failure
Slide 90
5. Tests and models of connections 90 Parametric Analyses
Parameters investigated : Type of connection : Fin plate, Web
cleats, Header plate Load ratio : 0.3, 0.5 and 0.7 Duration of the
fire : Short (ISO) or Long (60 min) Beam span : 6 m (IPE 300) or 12
m (IPE 550)
Slide 91
5. Tests and models of connections 91 Parametric Analyses : Fin
plate connections FEM model - Source : Corus Ltd Bilinear Fibres
ModelAbaqus Model
Slide 92
5. Tests and models of connections 92 Parametric Analyses : Web
cleats connections FEM model - Source : CTICM Bilinear Fibres
ModelANSYS Model d >> L/20
Slide 93
5. Tests and models of connections 93 Parametric Analyses :
Header plate connections FEM model - Source : Corus Ltd Bilinear
Fibres ModelAbaqus Model
Slide 94
5. Tests and models of connections 94 Parametric Analyses :
Conclusions Influence of ductility classes (design + T max ) :
ratio resistance of bolts in shear/resistance of beam web in
bearing higher for web cleats than fin plates. Bolts situated close
to the top flange increase the fire resistance but this effect is
counter-balanced by failures during cooling phase Cases with large
deflections (d > L/20) at the end of the heating phase should be
rejected
Slide 95
5. Tests and models of connections 95 Additional cases : Fin
plate connections K = 5%K = 12%
Slide 96
5. Tests and models of connections 96 Proposed design procedure
for simple connections Evolution of temperature profiles (cfr. part
2) Multiplication of w by 1.1 (restraints) Evaluation of the time
of fire resistance t 1 (following EN) Evaluation of cooling
Verification that cooling *t 1 > t heating 1. Heating phase
Slide 97
5. Tests and models of connections 97 Proposed design procedure
for simple connections 2. Cooling phase T bottom flange < T lim
at the end of heating phase or w > w lim or The resistance of
the brittle components is higher than the ultimate resistance of
the weakest ductile component (accounting for k nr ) multiplied by
1.2 NO CLASS B Recommendation n1 : Recommendation n2 : The
resistance of the brittle components is higher than the plastic
resistance of the weakest ductile component (accounting for k nr )
multiplied by 1.2 NO CLASS C Fin plate : w lim = 0.35 Web cleats :
w lim = 0.25 Header plate : w lim = 0.45
Slide 98
5. Tests and models of connections 98 Proposed design procedure
for simple connections 3. Summary CLASS A during cooling : t
heating w Inacceptable Heating w lim t(T lim ) Acceptable CLASS B
during cooling : CLASS C during cooling : Inacceptable Inacceptable
Cooling
Slide 99
5. Tests and models of connections 99 Proposed design procedure
for simple connections K = 3%K = 10% Fin-plate connections
Slide 100
5. Tests and models of connections 100 General Material Law On
the contrary of Bilinear F.M., the Nonlinear F.M. allows an
automatic detection of connection failures !
Slide 101
5. Tests and models of connections 101
Slide 102
5. Tests and models of connections 102 Heating PhaseCooling
Phase
Slide 103
5. Tests and models of connections 103
Slide 104
5. Tests and models of connections 104
Slide 105
5. Tests and models of connections 105
Slide 106
5. Tests and models of connections 106 Joint represented by
Nonlinear Fibres Model
Slide 107
5. Tests and models of connections 107 Component-based models
and material laws defined for the modelling of simple connections
under natural fire Bilinear Fibres Models and Nonlinear Fibres
Models validated against experimental tests and other numerical
simulations (solid models). Differences by the degree of
difficulty, the field of application and the ability to predict
connection failures Predominent influence of ductility on the
occurrence of connection failures design procedure proposed.
Slide 108
Academic year 2009-2010 108
Slide 109
6. General Conclusions 109 Proposal of new simple methods for
the prediction of temperature in 2D- beam sections and 3D-joint
zones covered by a concrete slab and calibration on numerical
results Validation against experimental tests performed at the
University of Manchester of a model built in SAFIR for the
prediction of internal forces in axially- and
rotationally-restrained beams under fire conditions Adaptations to
the simplified method developed by Yin and Li for predicting
bending moments profiles in axially- and rotationally- restrained
beams during heating and cooling phases of a fire and extension to
joints with a bilinear moment-rotation diagram Treatment of results
of tests performed on bolts and welds under fire.
Slide 110
6. General Conclusions 110 Development of analytical models for
bolts (tension or shear) and welds during the heating and cooling
phases of a fire Definition of two models and material laws for
modelling the action of simple steel connections under natural fire
conditions Definition of failure criteria for connections modelled
by Bilinear Fibres Models and validations against experimental
tests and numerical results obtained with more complex models
Realisation of parametric analyses using the Bilinear Fibres Models
for fin plate, double web cleats and header plate connections and
definition of design procedures to avoid connection failures
Slide 111
6. General Conclusions 111 Development of Nonlinear Fibres
Models for fin plate connections and validation against
experimental results of isothermal tests performed on isolated
joints (Sheffield) and a fire test performed on a sub-structure
(Delft) Application of the Nonlinear Fibres Models to a large-scale
steel structure with fin plate connections
Slide 112
6. General conclusions 112 By use of quite simple methods that
does not require FE models, possibility to predict distribution of
temperature in beams and joints covered by a concrete slab The use
of simplified methods for predicting internal forces in joints
under natural fire is limited to cases where the behaviour of
joints is bilinear and constant The influence of heating-cooling
cycles on the resistance and the ductility of bolts and welds
should be considered (k nr,b,min = 0.6 ; k nr,w,min = 0.8)
force-displacement models for bolts
Slide 113
6. General conclusions 113 The action of simple connections in
steel structures under natural fire may be represented by fibre
models, able to predict failures The ductility of connections has a
major influence on the occurrence of connection failures classes of
ductility
Slide 114
6. General Conclusions 114 Validation of the Heat Exchange
Method against experimental results (beam-slab contact) + protected
members Analysis of the reversibility of deformations in carbon
steel elements subjected to a heating-cooling cycle Integration of
group effects and instability phenomena into numerical models for
connections Definition of an adimensional fibre element for
representing the action of joints following the Component Method
Extension of this work to composite joints (tests available, models
adapted). Attention should be paid to the concept of collaborating
width)
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